1. Field of the Invention
The present invention relates to digital image and video processing. More specifically, the present invention relates to methods of noise reduction for interlaced digital video stream.
2. Discussion of Related Art
Due to advancing semiconductor processing technology, integrated circuits (ICs) have greatly increased in functionality and complexity. With increasing processing and memory capabilities, many formerly analog tasks are being performed digitally. For example, images, audio and even full motion video can now be produced, distributed, and used in digital formats.
FIG. 1 is an illustrative diagram of a portion of interlaced digital video stream 100 most often used in television systems. Interlaced digital video stream 100 comprises a series of individual fields 100_1 to 100_N, of which the first ten fields are shown. Even fields contain even numbered rows while odd fields contain odd numbered rows. For example if a frame has 400 rows of 640 pixels, the even field would contains rows 2, 4, . . . 400 and the odd field would contains rows 1, 3, 5, . . . 399 of the frame. In general for an interlaced video stream each field is formed at a different time. For example, an interlaced video capture device (e.g. a video camera) captures and stores the odd scan lines of a scene at time T as field 100_1, then the video capture device stores the even scan lines of a scene at time T+1 as field 100_2. The process continues for each field.
FIG. 2 illustrates a conventional noise reduction system 200 having a digital buffer 210, a noise reduction unit 220, and a deinterlacer 230. Digital buffer 210 stores portions of an input interlaced video stream I_IVS. Typically, digital buffer 210 is configured to store an integer number of fields from input interlaced video stream I_IVS. In general, video streams are stored in YUV format, where Y is the luminance, and U and V are chrominance values. Noise reduction unit 220 reads image data from digital buffer 210 as appropriate for the noise reduction algorithm and generates an interlaced noise reduced digital video stream INRDVS which is provided to deinterlacer 230. Deinterlacer 230 processes corresponding fields to generate progressive video frames and output deinterlaced video stream O_DVS, which can be displayed on a progressive digital video device (not shown).
Although digital images generally provide higher noise immunity, most digital images in digital video streams are converted from analog video streams. The original analog video stream may contain noise from various sources. For example, modulation, wireless transmission and demodulation of TV signals may introduce Gaussian-like noise. Furthermore, even analog video transferred over transmission lines may have Gaussian-like noise due to magnetic fields around the transmission lines. In addition, the digitalizing process may inadvertently amplify minor noise problems in the analog video stream.
Hence, there is a need for a noise filtering method or system to reduce noise in a digital image. Furthermore, noise filtering in a digital video stream must be performed quickly to match the frame rate of the digital video stream.